This invention relates to switches and more particularly to an electrical switch suitable for use in an electrical circuit operable for actuating the inflation of an airbag in a motor vehicle.
In the prior art, electrical circuits operable for actuating the inflation of airbags in vehicles have utilized mercury switches for actuating inflation mechanisms. In such switches, there typically has been provided an inclined tube having a globule of mercury normally positioned at a lower front end thereof and a set of electrical contacts at an upper rear end thereof. Whenever the vehicle is caused to decelerate rapidly, as upon impact, inertia causes the mercury globule to displace rearwardly and interconnect the set of contacts thus closing the airbag inflation actuating circuit. Such switches, however, have been found not to be entirely satisfactory in that the closing time is adversely affected by the surface tension of the mercury which has the effect of the mercury globule adhering to the contacts.
More recently, there has been developed an improved switch for such circuitry consisting of a tubular member provided with a pair of circular end plates having diameters greater than the diameter of the tubular member, a pair of reed relay contacts, each mounted on an end plate, projecting inwardly therefrom substantially axially relative to the tubular member and having the inner opposed ends thereof normally spaced apart transversely, an annular permanent magnet mounted on the tubular member and freely displaceable along a portion of the length thereof, and a helical spring mounted on the tubular member and between one end plate and the annular permanent magnet to yieldably bias the permanent magnet away from a point along the tubular member at which the magnetic field of the magnet would cause the reed contacts to engage and thus close a circuit. In the operation of such switches, whenever the vehicle incurs a sudden deceleration, such as upon impact, the inertia of the permanent magnet will cause it to displace forwardly along the length of the tubular member, against the biasing action of the helical spring, to a position where the magnetic field of the magnet causes the reed contacts to close.
The principal disadvantage of such switches is that their closing times are considerably less than those of mercury switches. In principle, it would be possible to increase the closing times of such switches by increasing the mass of the permanent magnet or by decreasing the biasing force. This, however, would result in the response threshold for the switches to approach lower decelerations. The switch would become more sensitive and thus not be effective for safety switch applications. It thus has been found to be desirable to provide such a switch in which the time in which the contacts are closed is increased without correspondingly decreasing the response threshold time.
Accordingly, it is the principal object of the present invention to provide an improved electrical switch.
Another object of the present invention is to provide an improved electrical switch suitable for use in electrical circuitry operable for actuating the inflating mechanism of an airbag of a vehicle.
A further object of the present invention is to provide an improved deceleration switch suitable for use in vehicle airbag systems.
A still further object of the present invention is to provide an improved deceleration switch for use in a vehicle airbag system in which a magnetic element is adapted to displace against the biasing force of a spring upon a predetermined deceleration of the vehicle, as upon impact, to close a set of contacts in which the closing time of the switch is increased without correspondingly decreasing the response threshold time of the switch.